Actually, in optical communication, an optical signal that has been transmitted at a high speed is once converted into an electrical signal, which is subjected to data processing in an electronic circuitry, and the processed data signal is then reconverted into an optical signal to be transmitted. This incapability to achieve direct control of an optical signal with another optical signal has limited the efficiency of optical signal processing.
In such as high-speed processing of bulk information and broad-band services that provide information such as dynamic image communication and picture image transmission or distribution, using fiber-optic communication capable of broad-band efficient and high-speed data transmission or transfer, there is expected technique for processing an optical signal by another optical signal. In electronics, for example, there have been required functional elements (signal amplifying elements) equivalent to transistors, that is, optical function devices capable of controlling an optical signal directly with another optical signal.
The present inventors has suggested an optical function element and an optical function device that are configured to output an amplified signal light by controlling an input light using a control light as disclosed in WO02/086616 A1, Patent Document 1. It discloses a three-terminal optical function element to output a processed signal light of a first wavelength after such as a switching processing by a control light, as follows. A first input light at the first wavelength and a bias light at a second wavelength having a predetermined intensity are input to a first semiconductor optical amplifying element. A light at a second wavelength selected from the output light from the first semiconductor optical amplifying element and another laser light (control light) at another wavelength, for example, the first wavelength, are coupled together and input into a second semiconductor optical amplifying element. A portion of the output light from the second semiconductor optical amplifying element is returned by positive feedback, and an output signal light at the first wavelength is selected from the other portion.
Patent Document 1: WO02/086616 A1